Limited availability and high cost of petroleum sources has led to the increased cost of producing basic commodity chemicals and their derivatives from such petroleum sources. As a result, various alternative competing technologies have been developed and commercially implemented in order to produce these chemicals from non-petroleum sources at a competitive cost.
One such technology involves catalytically converting methanol to olefins (MTO). Methanol is a readily available feedstock, which can be manufactured both from petroleum as well as non-petroleum sources, for example, by fermentation of biomass or from synthesis gas.
A typical MTO process, as disclosed in U.S. Pat. No. 4,499,327, which is hereby incorporated in its entirety, involves contacting methanol with a zeolite catalyst, such as an aluminosilicate, under conditions of temperature and pressure in order to produce light olefins, such as ethylene. Ethylene is an extremely valuable commodity chemical for producing various derivatives, such polyethylene, used in many commercial as well as consumer products and applications.
Before ethylene produced by an MTO process can be sold and used, it is necessary to employ a process which recovers the ethylene component in a desirable, ethylene rich stream by separating it from other components and impurities. For example, depending on the feedstock composition, the reaction conditions, and the extent of side reactions, an MTO effluent can contain other light olefins and diolefins, and light paraffins such as methane and ethane.
One process for the separating and recovering of ethylene from an MTO process effluent involves the use of flash stages and distillation at cryogenic temperatures, as described in U.S. Pat. Nos. 7,166,757 and 4,499,327. The cryogenic separation can be very expensive due to both the capital cost of the specialized vessel metallurgy and refrigeration equipment, and the operating costs, including compression and cooling for the energy-intensive chill train. The compression and cooling may be provided by, for example, an ethylene refrigerant provided by an ethylene refrigeration compressor from within the recovery unit or from another nearby processing unit. The cryogenic temperatures may also result in the undesirable formation of N2O3 from any NOx in the MTO process effluent.
Another process for separating and recovering ethylene from an MTO process effluent, at non-cryogenic temperatures, is disclosed in US20100105973. While operating at higher temperatures and potentially avoiding formation of N2O3, the higher operating temperatures may limit the extent of recovery of ethylene and propylene from the MTO effluent.